The clinical areas of primary focus of the NIDCR study include the neurological, renal, endocrine, immunological, and numerous psychological conditions. The oral health examination included an assessment of caries, soft-tissue lesions, and a complete tooth and surface based inventory of dental restorative materials, including amalgams. This study, a collaboration with the U.S. Air Force, involves a multi-disciplinary team of mercury toxicologists, neurologists, psychologists, immunologists, statisticians, laboratory experts, other medical specialists and clinical dentists. The mean age of the 1,166 study participants was 52.8 years. Overall, 5.2 percent of the participants were edentulous. Dentate individuals averaged 19.9 amalgam surfaces per person, with amalgam contributing slightly more than one-half of all restored surfaces in dentate individuals. We estimate that this cohort has a higher exposure to dental amalgams than their age-matched U.S. male population. The total mercury level in urine was 3.1 mg per liter and 2.6 mg for whole blood. A clear dose-response was observed between the levels of mercury (total and inorganic) in urine and the amount of exposure to amalgam. The frequency of abnormal neurological conditions was very low, with most response measures affecting between 1 and 5 percent of these participants. There was no evidence of a clear dose-response relationship between amalgam exposure and the level of neurological abnormalities. A couple of specific response measures associated with amalgam exposure, but these were inconsistently manifested among various subgroups, being both positively or negatively associated with amalgam levels. As a consequence of external expert reviews further analyses incorporating important exclusionary criteria (previously unavailable, but recently incorporated into the databases) are in the final stages. The major findings of this study will be important to validate. A second examination of the full study cohort of 2,200 participants is underway in an attempt to better delineate the significance of the associations detected on the first cycle. These examinations were completed in the spring of 1998.